U.S. patent number 6,131,751 [Application Number 08/845,843] was granted by the patent office on 2000-10-17 for counter weight handling system and boom parking device.
This patent grant is currently assigned to Manitowoc Crane Group, Inc.. Invention is credited to David J. Pech, Alan E. Pleuss, Kenneth J. Porubcansky.
United States Patent |
6,131,751 |
Pech , et al. |
October 17, 2000 |
Counter weight handling system and boom parking device
Abstract
A crane having an upper works rotatably mounted on a lower works
and a boom pivotally mounted on the upper works, wherein the crane
further comprises an apparatus and method for lifting, positioning,
and assembling a counter weight to the upper works. The apparatus
and method includes pivotally connecting a counter weight pivot
frame between the counter weight and the upper works and lifting
the counter weight into position with the hydraulic boom hoist
cylinder. The crane further comprises a boom parking device.
Inventors: |
Pech; David J. (Manitowoc,
WI), Pleuss; Alan E. (Manitowoc, WI), Porubcansky;
Kenneth J. (Whitelaw, WI) |
Assignee: |
Manitowoc Crane Group, Inc.
(Reno, NV)
|
Family
ID: |
26688329 |
Appl.
No.: |
08/845,843 |
Filed: |
April 23, 1997 |
Current U.S.
Class: |
212/178;
212/195 |
Current CPC
Class: |
B66C
23/36 (20130101); B66C 23/62 (20130101); B66C
23/74 (20130101); B66C 23/82 (20130101) |
Current International
Class: |
B66C
23/36 (20060101); B66C 23/00 (20060101); B66C
23/74 (20060101); B66C 23/62 (20060101); B66C
23/82 (20060101); B66C 023/74 () |
Field of
Search: |
;212/279,178,195,196,197,198 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
0 354 167 |
|
Feb 1990 |
|
EP |
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1 247 585 |
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Aug 1967 |
|
DE |
|
23 40 171 |
|
Feb 1975 |
|
DE |
|
128938 |
|
Aug 1993 |
|
JP |
|
Primary Examiner: Brahan; Thomas J.
Attorney, Agent or Firm: Brinks Hofer Gilson & Lione
Parent Case Text
This application is a continuation-in-part of U.S. provisional
application Ser. No. 60/016,226, entitled Self-Assembling Boom
Hoist Cylinder Crane, filed Apr. 26, 1996; and a
continuation-in-part of U.S. provisional application Ser. No.
60/041,555, entitled Boom Hoist Cylinder Crane, filed Apr. 16,
1997.
Claims
We claim:
1. A crane having an upper works rotatably mounted on a lower works
and a boom pivotally mounted on the upper works comprising:
a) a counter weight removably connected to the upper works; and
b) a counter weight handling system for removing and lowering said
counter weight from said upper works, said counter weight handling
system comprising a counter weight pivot frame having a first end
and a second end, said first end being pivotally connected to the
upper works and said second end being pivotally connected to the
counter weight, said counter weight pivot frame being pivotable
through a vertical arc around an axis formed by the connection of
the first end of the counter weight pivot frame to the upper works,
said counter weight handling system further comprising a hydraulic
cylinder pendently connected to said second end of said counter
weight pivot frame, wherein said hydraulic cylinder is retracted to
lower said counter weight from said upper works.
2. A crane according to claim 1 wherein the counter weight pivot
frame comprises a first strut and a second strut, said struts each
having a first end and a second end.
3. A crane according to claim 2 wherein the first end of the first
strut is pivotally connected to a first side of the upper works,
the first end of the second strut is pivotally connected to a
second side of the upper works, and the second end of the first
strut and second end of the second strut are each pivotally
connected to the counter weight.
4. A crane according to claim 1 wherein the counter weight pivot
frame comprises a "U" shaped frame having two legs connected by a
cross-member.
5. A crane according to claim 4 wherein each leg of the frame is
pivotally connected between the upper works and the counter
weight.
6. A crane according to claim 1 wherein the counter weight is
supported by a counter weight tray, said tray having a plurality of
pendants pivotally connected between the second end of said counter
weight pivot frame and the counter weight tray.
7. A crane according to claim 6 wherein the pendants are connected
to the counter weight tray in a manner that causes the counter
weight to tilt rearwardly from the upper works of the crane as the
counter weight is lowered from the upper works.
8. A crane according to claim 6 wherein the counter weight tray is
removably connected to the upper works by a plurality of hooks on
said counter weight tray that engage a plurality of pins on said
upper works.
9. A crane according to claim 6 wherein the counter weight tray
comprises a guide roller for guiding said counter weight tray into
an engaged position connected to said upper works.
10. A crane according to claim 1 wherein a wire rope pendant is
used to pendently connect the hydraulic cylinder to the second end
of said counter weight pivot frame.
11. A crane according to claim 1 wherein the counter weight is
suspended by the hydraulic cylinder and the counter weight pivot
frame while said counter weight is removed and lowered from said
upper works.
12. A crane according to claim 1 wherein the hydraulic cylinder is
pivotally connected between a mast and the upper works, said mast
comprising a first end pivotally connected to said upper works and
a second end pivotally connected to an end of said hydraulic
cylinder.
13. A crane according to claim 12 wherein the hydraulic cylinder is
connected to the counter weight by a wire rope pendant, said wire
rope pendent being connected to the end of said hydraulic cylinder
that is pivotally connected to the second end of said mast.
14. A boom hoist cylinder crane having an upper works rotatably
mounted on a lower works, said crane further comprising:
a) a mast having a first end and a second end, said first end being
pivotally connected to said upper works;
b) a hydraulic cylinder having a first end and a second end, said
first end being pivotally connected to said upper works and said
second end being
pivotally connected to the second end of said mast;
c) a boom pivotally mounted on said upper works and pendently
connected to either the second end of said mast or the second end
of said hydraulic cylinder, said boom being pivotable through an
angle relative to said upper works, said angle being controlled by
extension or retraction of said hydraulic cylinder;
d) a counter weight removably connected to said upper works;
and
e) a counter weight handling system for moving said counter weight
between a first position connected to said upper works and a second
position disconnected from said upper works, said counter weight
handling system comprising a counter weight pivot frame having a
first end and a second end, said first end being pivotally
connected to the upper works, said second end being pivotally
connected to the counter weight and pendently connected to the
hydraulic cylinder, said counter weight pivot frame being pivotable
through a vertical arc around an axis formed by the connection of
the first end of the counter weight pivot frame to the upper works,
wherein said hydraulic cylinder is retracted to move said counter
weight from said first position to said second position.
15. A boom hoist cylinder crane according to claim 14 wherein the
counter weight is supported by a counter weight tray, said tray
having a plurality of counter weight pendants pivotally connected
between the second end of said counter weight pivot frame and the
counter weight tray.
16. A boom hoist cylinder crane according to claim 15 wherein the
counter weight pendants are connected to the counter weight tray in
a manner that causes the counter weight to tilt rearwardly from the
upper works of the crane as the counter weight is lowered from the
upper works.
17. A boom hoist cylinder crane according to claim 15 wherein the
counter weight tray is removably connected to the upper works by a
plurality of hooks on said counter weight tray that engage a
plurality of pins on said upper works.
18. A boom hoist cylinder crane according to claim 15 wherein the
counter weight tray comprises a guide roller for guiding said
counter weight tray into said first position connected to the upper
works.
Description
BACKGROUND OF THE INVENTION
The present application relates to construction equipment, such as
cranes. In particular, the present application relates to a crane
having several unique and inventive aspects, such as a hydraulic
boom hoist cylinder, a hydraulic circuit to control the hydraulic
boom hoist cylinder, a multiple position wire rope guide, and a
counter weight positioning mechanism. The present application also
relates to a method of self-assembling the boom hoist cylinder
crane.
Construction equipment, such as cranes or excavators, often must be
moved from one job site to another. Moving a crane or an excavator
can be a formidable task when the machine is large and heavy. For
example, highway limits on vehicle-axle loads must be observed and
overhead obstacles can dictate long, inconvenient routings to the
job site.
One solution to improving the mobility of large construction
machines, such as cranes, is to disassemble them into smaller, more
easily handled components. The separate components can then be
transported to the new job site where they are reassembled.
The typical practice has been to use an assist crane to disassemble
the crane into the separate components. The assist crane is then
used to load the components onto their respective transport
trailers. Once at the new job site, another assist crane is used to
unload the components and reassemble the crane. As the components
for a large crane can weigh as much as 80,000 lbs., the capacity of
the assist crane required represents a very significant transport
expense.
As a result, designers have attempted to develop self-handling
systems for assembling and disassembling cranes. The majority of
the self-handling systems developed thus far have been directed to
smaller cranes which need to be disassembled into only a few
components.
The development of self-handling systems for larger cranes,
however, has met with limited success. One reason for this is that
larger cranes need to be disassembled into numerous components,
thus requiring time-consuming disassembly and reassembly
procedures. For example, a large capacity crane typically uses a
complicated and cumbersome rigging system to control the angle of
the boom. Boom rigging system components such as the equalizer, the
backhitch, and wire rope rigging are heavy and difficult to
disassemble for transport. Another reason for the limited success
of prior art self-assembling cranes is that they typically rely on
additional crane components that are used only for assembling and
disassembling the crane. For example, some self-assembling cranes
require additional wire rope guides and sheaves on the boom butt so
that a load hoist line can be used with the boom butt to lift
various crane components during the assembly process. An example of
one prior art method for disassembling a typical large capacity
crane is disclosed in U.S. Pat. No. 5,484,069.
It is therefore desirable to provide a crane and method of
self-assembly which reduces the number of parts which must be
derigged and removed to disassemble the crane for transport. In
addition, it is desirable to
eliminate redundant components which are only used during the crane
assembly process.
SUMMARY OF THE INVENTION
In preferred aspects, the invention provides an apparatus and
method for self-assembling a counter weight to a crane. The crane
comprises an upper works rotatably mounted on a lower works, a mast
pivotally connected to a hydraulic cylinder, a boom supported by
the mast and the hydraulic cylinder, a counter weight, and a
counter weight pivot frame having a first end and a second end,
said first end of the counter weight pivot frame being pivotally
connected to the upper works. The method comprises the following
steps. First, the counter weight is positioned behind the upper
works. Next, the counter weight is pivotally connected to the
second end of the counter weight pivot frame. The counter weight is
then pendently connected to either the mast or the hydraulic
cylinder at a location near the connection between the mast and the
hydraulic cylinder. The hydraulic cylinder is then extended to
raise the counter weight. Finally, the counter weight is secured in
its operating position.
The counter weight of a large capacity crane can weigh as much as
150,000 lbs., requiring a substantial size crane just to lift and
guide it into its operating position. The self-assembling counter
weight apparatus and method of the present invention improves over
prior art by providing a self lifting and guiding system.
In another aspect, the present invention further comprises a boom
parking device. The boom parking device comprises a pendant
connected between the mast and the rear of the upper works. The
pendant transfers the weight of the boom to the counter weight and
other components attached to the rear of the upper works. Once
connected, the hydraulic pressure can be released from the
hydraulic cylinder which supports the boom.
These and other advantages, as well as the invention itself, will
become apparent in the details of construction and operation as
more fully described and claimed below. Moreover, it should be
appreciated that several aspects of the invention can be used with
other types of machines or equipment.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a right side elevational view of a complete boom hoist
cylinder crane incorporating a counter weight positioning mechanism
and a boom parking device made in accordance with the teachings of
this invention.
FIG. 2 is a partial right side elevational view of the boom hoist
cylinder crane showing some of the internal components of the crane
upper works.
FIGS. 3-7 are right side elevational views of the crane in
sequential stages of lower works assembly.
FIGS. 8-10 are right side elevational views of the crane in
sequential stages of upper counter weight assembly.
FIGS. 11-12 are partial right side elevational views of the crane
in sequential stages of the wire rope guide repositioning.
FIGS. 13-15 are right side elevational views of the crane in
sequential stages of boom top and boom insert assembly.
FIG. 16 is a partial right side elevational view of the crane with
the boom parking device engaged.
FIGS. 17-20 are partial right side elevational views of the crane
in sequential stages of the repositioning of an alternative
embodiment of the wire rope guide.
FIG. 21 is a schematic of the hydraulic circuit which controls the
hydraulic boom hoist cylinder.
DETAILED DESCRIPTION OF THE DRAWINGS AND PREFERRED EMBODIMENTS OF
THE INVENTIONS
While the present invention will find application in all types of
cranes or construction machines, the preferred embodiment of the
invention is described in conjunction with the boom hoist cylinder
crawler crane 10 of FIGS. 1 and 2. The boom hoist cylinder crawler
crane 10 includes an upper works 12 having a rotating bed 14 which
is rotatably connected to a lower works 16 by a swing bearing 18.
The lower works 16 includes a car body 20, car body counter weights
22, and two independently powered crawlers 24.
The upper works includes a boom 26 pivotally connected to the upper
works 12. The boom 26 comprises a boom top 28 and a tapered boom
butt 30. The boom 26 may also include one or more boom inserts 32
connected between the boom top 28 and the boom butt 30 to increase
the overall length of the boom 26. The angle of the boom 26 is
controlled by a pair of hydraulic boom hoist cylinders 34 pivotally
connected to the upper works 12. A mast 36 is pivotally connected
between the piston rods 38 of the hydraulic boom hoist cylinders 34
and the upper works 12. The boom hoist cylinders 34 are connected
to the upper works 12 at a point preferably near the lower end of
the boom hoist cylinders 34, but may be connected to the upper
works 12 at any point along the bore 40 of the boom hoist cylinders
34. The boom 26 is connected to the piston rods 38 of the hydraulic
boom hoist cylinders 34 and the mast 36 by one or more boom
pendants 42. The boom pendants 42 may be connected to either the
mast 36 or the piston rods 38 of the hydraulic boom hoist cylinders
34, but preferably are connected at a point near the connection
between the mast 36 and the piston rods 38 of the hydraulic boom
hoist cylinders 34. A boom backstop 44 is provided to prevent the
boom 26 from exceeding a safe operating angle.
The position of the boom 26 is controlled by the hydraulic boom
hoist cylinders 34. The mast 36 supports the connection between the
hydraulic boom hoist cylinders 34 and the boom pendants 42 at a
location that is distanced from the axis of the boom 26 to optimize
the forces in the boom pendants 42 and the hydraulic boom hoist
cylinders 34. This arrangement also permits the hydraulic boom
hoist cylinders 34 to impart a force having a component that is
perpendicular to the axis of the boom 26. This force is transferred
to the end of the boom 26 by the boom pendants 42.
Extending the hydraulic boom hoist cylinders 34 decreases the angle
between the front of the boom 26 and the ground. Conversely,
retracting the hydraulic boom hoist cylinders 34 increases the
angle between the front of the boom 26 and the ground. Under normal
operating conditions, the hydraulic boom hoist cylinders 34 and the
boom pendants 42 are in tension from the weight of the boom 26 and
any load being lifted by the crane 10. Conversely, the mast 36 is
in compression under normal operating conditions.
As best seen in FIG. 2, the mast 36 and the hydraulic boom hoist
cylinders 34 are pivotally connected to the top of the rotating bed
14 of the upper works 12. The connection of the boom hoist
cylinders 34 to the rotating bed 14 is at a position that is behind
and higher in elevation than the connection of the mast 36 to the
rotating bed 14. As best seen in FIGS. 3-4, this configuration
allows the hydraulic boom hoist cylinders 34 and the mast 36 to be
lowered to an approximately horizontal position on top of the upper
works 12 when the crane 10 has been disassembled for transport. It
is important to minimize the overall height of the disassembled
crane 10 so that highway height restrictions will not be violated
during transport to and from the job site. This configuration also
allows the hydraulic boom hoist cylinders 34 to control the boom 26
even when the boom has been lowered to an angle which is below
horizontal.
In the crane 10 of the preferred embodiment shown, two hydraulic
boom hoist cylinders 34 are used in tandem. However, it should be
understood that any number of hydraulic boom hoist cylinders 34,
including a single hydraulic cylinder, can be used in the above
described arrangement. The hydraulic boom hoist cylinders 34 must
have sufficient capacity to function under the loads generated by
the operation of the crane 10 when lifting objects. The pistons 38
of the hydraulic boom hoist cylinders 34 should also have a stroke
of sufficient length so as to be lowered on top of the upper works
12 for disassembly and transport without requiring disconnection
from the mast 36. In the preferred embodiment shown, which is for a
crane having a rating of 120-175 tons, each hydraulic boom hoist
cylinder 34 has a stroke of 160 inches.
In the preferred embodiment shown, the mast 36 is comprised of a
frame. Alternatively, the mast 36 can be comprised of a pair of
individual struts. The mast 36 should not interfere with the
operation of the load hoist lines 46 or the boom backstop 44.
The upper works 12 further includes one or more load hoist lines 46
for lifting loads. Each load hoist line 46 is reeved around a load
hoist line drum 48 supported on the rotating bed 14 of the upper
works 12. The load hoist line drums 48 are rotated to either pay
out or retrieve the load hoist lines 46. The load hoist lines 46
pass through a wire rope guide 50 attached to the upper interior
side of the boom butt 30 and are reeved around a plurality of boom
top sheaves 52 located at the upper end of the boom top 28. The
wire rope guide 50 prevents the load hoist lines 46 from
interfering with the lattice structure of the boom 26. A hook block
54 is typically attached to each load hoist line 46.
As best seen in FIG. 2, the upper works 12 further includes a power
plant 56, such as a diesel engine, enclosed by a power plant
housing 58 and supported on a power plant base 60. The power plant
base 60 is connected to the rear of the rotating bed 14. Connected
to the power plant base 60 is a upper counter weight assembly 62
comprising a plurality of counter weights 64 supported on a counter
weight tray 66. The power plant 56 supplies power for the various
mechanical and hydraulic operations of the crane 10, including
movement of the crawlers 24, rotation of the rotating bed 14,
rotation of the load hoist line drums 48, and operation of the
hydraulic boom hoist cylinders 34. The mechanical and hydraulic
connections between the power plant 56 and the above-listed
components have been deleted for clarity. Operation of the various
functions of the crane 10 are controlled from the operator's cab
68.
As best seen in FIGS. 11 and 12, the wire rope guide 50 comprises
at least one positionable sheave 80. The positionable sheave 80 is
movable between a first position on the end of the boom butt 30
(see FIG. 11) and a second position on the upper interior side of
the boom butt 30 (see FIG. 12). As will be described in greater
detail below in connection with the preferred method of assembling
the crane 10, locating the positionable sheave 80 in the first
position on the end of the boom butt 30 allows a load hoist line 46
to be used for lifting objects prior to assembling the boom top 28
and any boom inserts 32 to the boom butt 30 of the crane 10. When
in this position (as best seen in FIGS. 5-7), the wire rope guide
50 prevents the load hoist line 46 from interfering with the
lattice structure of the boom butt 30 by guiding the load hoist
line 46 around the end of the boom butt 30. The wire rope guide 50
also minimizes eccentric loading of the boom butt 30 when using the
load hoist line 46 to lift objects.
When the boom top 28 and any boom inserts 32 are assembled to the
crane 10, the positionable sheave 80 is located on the upper
interior side of the boom butt 30 (see FIG. 1). When in this
position (see FIG. 1), the wire rope guide 50 prevents the load
hoist lines 46 from interfering with the boom 26 by maintaining a
separation between the load hoist lines 46 and the boom top 28 and
any boom inserts 32 irrespective of the boom angle.
As best seen in FIGS. 11 and 12, the positionable sheave 80 is
supported by a pivotal frame 82 pivotally connected to the boom
butt 30 at or near the interior edge 84 adjoining the upper
interior side and the end of the boom butt 30. The wire rope guide
50 of the preferred embodiment also comprises a stationary sheave
86 located on the upper interior side of the boom butt 30. The
stationary sheave 86 is supported by a stationary frame 88 attached
to the interior side of the boom butt 30. The stationary frame 88
also supports the pivotal frame 82 when the positionable sheave 80
is in the second position on the upper interior side of the boom
butt 30 (as shown in FIG. 12). When the positionable sheave 80 is
in the first position on the end of the boom butt 30, the pivotal
frame 82 is connected to the end of the boom butt 30 at or near the
exterior edge 90 adjoining the upper exterior side and the end of
the boom butt 30 (see FIG. 11).
An alternative embodiment of a positionable wire rope guide, also
called a load hoist line guide, is shown in FIGS. 17-20. As best
seen in FIG. 17, the wire rope guide 300 of the alternative
embodiment is comprised of a first sheave 302 and a second sheave
304. The first sheave 302 is supported by a first frame 306 and the
second sheave 304 is supported by a second frame 308. The first
frame 306 is pivotally connected to one edge of the end of the boom
butt 30. The first frame 306 is also pivotally connected to the
second frame 308. The second frame 308 is removably connected to
the opposite edge of the end of the boom butt 30 when the wire rope
guide 300 is positioned on the end of the boom butt 30. In the
alternative embodiment shown, a collapsible strut 310 is connected
between the first frame 306 and the second frame 308 to maintain
rigidity between the first sheave 302 and the second sheave 304
when the wire rope guide 300 is positioned on the end of the boom
butt 30. A rigging platform 312 is also provided on the first frame
306 (see FIG. 20).
The crane 10 of the preferred embodiment also comprises a
self-handling system for assembling and disassembling the upper
counter weight assembly 62. As best seen in FIG. 8, the upper
counter weight assembly 62 self-handling system comprises a pair of
counter weight pendants 110 connected to a counter weight pivot
frame 114 by a pair of links 112. The function of these components
will be discussed in greater detail below with respect to the
procedure for self-assembly the crane 10 of the preferred
embodiment. However, these components are also used as a boom 26
parking device. As shown in FIG. 16, the angle of the boom 26 can
be secured while the crane 10 is not in use by connecting the
counter weight pendants 110 to the links 112. The links 112 and the
counter weight pivot frame 114 are both connected to the upper
counter weight assembly 62, which in turn is connected to the power
plant base 60. These connections are discussed in greater detail
below with respect to the procedure for self-assembly the crane 10
of the preferred embodiment. Once the counter weight pendants 110
are connected, the pressure in the hydraulic boom hoist cylinders
34 can be released to permit the weight of the boom 26 to be
carried by the upper counter weight assembly 62 and the power plant
56, thereby eliminating the need to maintain a constant pressure in
the hydraulic boom hoist cylinders 34 to maintain the angle of the
boom.
The preferred method of self-assembling the boom hoist cylinder
crawler crane 10 is best seen by referring to FIGS. 3-15 and the
description above.
Referring to FIG. 3, the disassembled boom hoist cylinder crawler
crane 10 is delivered to the job site on a transport trailer 100.
Additional components, such as the boom top 28, any boom inserts
32, the crawlers 24, the car body counter weights 22, and the upper
counter weight assembly 62, are delivered on separate transport
trailers (not shown) prior to their assembly to the crane 10.
Referring to FIGS. 3-4, the pistons 38 of the hydraulic boom hoist
cylinders 34 are retracted to raise the hydraulic boom hoist
cylinders 34 and the mast 36 up off of the transport trailer 100. A
boom butt pendant 102 is then connected between the end of the boom
butt 30 and the mast 36. In the preferred method of self-assembly,
the wire rope guide 50 is initially positioned on the end of the
boom butt 30. One end of the boom butt pendant 102 is then
connected to the mast 36 at a point near the connection between the
mast 36 and the boom hoist cylinders 34. The other end of the boom
butt pendant 102 is then connected to the pivotal frame 82 of the
wire rope guide 50. When not in use, the boom butt pendant 102
remains connected to, and is stowed on, the mast 36. The hydraulic
boom hoist cylinders 34 are then retracted an additional distance
to raise the boom butt 30 off of the transport trailer 100 (FIG.
4).
A plurality of jacking cylinders 104 attached to the car body 20
are swung into a position straddling the transport trailer 100. The
jacking cylinders 104 are then extended to raise the car body 20
off of the transport trailer 100. The transport trailer 100 can
then be removed.
Referring to FIGS. 5-6, a load hoist line 46 is reeved around the
stationary sheave 86 and the positionable sheave 80 of the wire
rope guide 50. A hook block 54 is rigged to the load hoist line 46.
The end of the load hoist line 46 is connected to boom butt 30. The
load hoist line 46 and the hydraulic boom hoist cylinders 34 are
now used to remove the crawlers 24 from a transport trailer 100 and
position them for attachment
to the car body 20. The hook block 54 can be raised or lowered by
rotating the load hoist line drum 48 to either pay out or retract
the load hoist line 46. The angle of the boom butt 30 can be
changed by either extending or retracting the hydraulic boom hoist
cylinders 34, thereby moving an object attached to the hook block
54 further from or closer to the crane 10. The position of the
upper works 12 relative to the car body 20 is controlled through
rotation of the swing bearing 18. Once a crawler 24 has been
properly positioned, it is then attached to the car body 20. A
method and apparatus for assembling the crawlers 24 to the car body
20 are disclosed in U.S. Pat. No. 5,427,256. Another method of
assembling the crawlers 24 to the car body 20 is disclosed in U.S.
patent application Ser. No. 07/762,764.
After both crawlers 24 have been attached to the car body 20, the
jacking cylinders 104 can then be retracted to lower the crane 10
onto the ground. The jacking cylinders 104 are then stored against
the side of the car body 20. In the alternative, the jacking
cylinders 104 can be removed from the crane 10.
Referring to FIG. 7, the crane 10 may now be used to position other
crane components for assembly to the crane 10. For example, the
load hoist line 46 and the hydraulic boom hoist cylinders 34 can be
used to position and assemble the car body counter weights 22 to
the car body 20.
The hydraulic boom hoist cylinders 34 are also used to assemble the
upper counter weight assembly 62 to the upper works 12. As best
seen in FIG. 8, the crane 10 is used to lift the upper counter
weight assembly 62 off of a transport trailer (not shown) and place
it on the ground behind the crane 10. A pair of counter weight
pendants 110 are then each attached to a link 112 connected to each
side of the counter weight pivot frame 114. One end of each counter
weight pendant 110 is pinned to the mast 36 at a point near the
connection between the hydraulic boom hoist cylinder 34 and the
mast 36. When not in use, the counter weight pendants 110 remain
connected to, and are stowed on, the mast 36 (see FIG. 7).
The counter weight pivot frame 114 of the preferred embodiment is
comprised of a U-shaped frame having the legs of the "U" connected
between the power plant base 60 and the upper counter weight
assembly 62. The cross-member which is connected between the legs
of the U-shaped frame provides rigidity to the structure.
Alternatively, the counter weight pivot frame 114 is comprised of a
pair of struts, one strut being pivotally connected to each side of
the power plant base 60.
As best seen in FIG. 8, the upper counter weight assembly 62 of the
preferred embodiment comprises a plurality of counter weights 64
supported on a counter weight tray 66. Attached to the interior of
each side of the counter weight tray 66 is a plurality of pendants
116.
In the preferred method of self-assembly, the crane 10 is
maneuvered to align the counter weight pivot frame 114 with the
upper counter weight assembly 62. The counter weight pivot frame
114 is then pinned to the pendants 116 attached to the counter
weight tray 66 (see FIG. 8).
As best seen in FIG. 9, the hydraulic boom hoist cylinders 34 are
then extended to lift the upper counter weight assembly 62 off of
the ground. As the upper counter weight assembly 62 is lifted
upwards by the hydraulic boom hoist cylinders 34, the counter
weight pivot frame 114 swings the upper counter weight assembly 62
through a vertical arc about the axis of the connection of the
counter weight pivot frame 114 to the upper works 12. The
connection of the pendants 116 to the counter weight pivot frame
114 is forward of the center of gravity of the upper counter weight
assembly 62 such that upper counter weight assembly 62 tilts toward
the rear of the crane 10 when suspended by the pivot frame 114.
As the upper counter weight assembly 62 is lifted into its
operating position on the rear of the upper works 12, a roller 118
engages the underside of the power plant base 60 (see FIG. 9A). As
the hydraulic boom hoist cylinders 34 are extended further, the
roller 118 guides the upper counter weight assembly 62 forward
until a hook 120 on each side of the counter weight tray 66 engages
a pin 122 on each side of the power plant base 60. The reward tilt
of the suspended upper counter weight assembly 62 permits the hooks
120 to clear the pins 122 during the lifting operation. Once the
hooks 120 engage the pins 122, the hydraulic boom hoist cylinders
34 are extended further until a pinning hole 124 located near the
rear of each side of the counter weight tray 66 is aligned with an
oval shaped hole 126 located on each side of the power plant base
60 (see FIG. 9B). A limit switch (not shown) prevents the hydraulic
boom hoist cylinders 34 from being over extended. A pin 128 is then
placed through the each pinning hole 124 and oval shaped hole 126
to secure the upper counter weight assembly 62 to the power plant
base 60. Once the pins 128 are in place, the hydraulic boom hoist
cylinders 34 are retracted to remove the tension in the counter
weight pendants 110 and the links 112. The counter weight pendants
110 are then disconnected from the links 112 and stowed on the mast
36. Likewise, the links 112 are stowed on the power plant base
60.
In the preferred method of assembly, at least one of the car body
counter weights 22 are assembled to the car body 20 prior to
assembling the upper counter weight assembly 62 to the upper works
12 to add stability to the crane 10. Installation of the second car
body counter weight 22 may interfere with the installation of the
upper counter weight assembly 62 to the upper works 12. If only one
of the car body counter weights 22 was installed prior to assembly
of the upper counter weight assembly 62 to the upper works 12, then
the second car body counter weight 22 should be installed at this
stage of the crane self-assembly method.
Referring to FIGS. 11-12, the wire rope guide 50 is relocated from
a first position on the end of the boom butt 30 to a second
position on the upper interior side of the boom butt 30. As best
seen in FIG. 11, the hydraulic boom hoist cylinders 34 are extended
to rest the boom butt 30 on the ground. Blocking 130 is placed
under the exterior edge 90 of the boom butt 30 to prevent the
ground from interfering with the wire rope guide 50. The hook block
54 and the load hoist line 46 are then derigged and removed from
the wire rope guide 50. A pin 132 which connects the pivotal frame
82 to the exterior edge 90 of the boom butt is then removed. The
hydraulic boom hoist cylinders 34 are then retracted to raise the
pivotal frame 82 in an upward arc about the pivotal connection of
the pivotal frame 82 to interior edge 84 of the boom butt 30. As
shown in FIG. 12, the pivotal frame 82 is positioned adjacent to
the stationary frame 88. The pivotal frame 82 is then connected to
the stationary frame 88 by installing a pin 134 through holes in
the pivotal frame 82 and the stationary frame 88.
The alternative embodiment of the positionable wire rope guide 300
shown in FIGS. 17-20 is relocated through a similar procedure. As
shown in FIGS. 17-18, pin 314 is removed from the collapsible strut
310 to allow the strut 310 to fold. Pin 316 is then removed to
release the connection between the second frame 308 and the end of
the boom butt 30. The hydraulic boom hoist cylinders 34 are then
extended to allow the first frame 306 to swing downwardly against
the stop 318.
Referring to FIGS. 17-18, the boom butt pendant 102 is disconnected
from the first frame 306 and reconnected to a lifting link 320 on
the second frame 308. A lifting link pin 322, which secures the
lifting link 320 when not in use, is removed to allow the lifting
link 320 to pivot with the boom butt pendant 102. The hydraulic
boom hoist cylinders 34 are then retracted to draw the second frame
308 upwards towards the first frame 306 by swinging the second
frame 308 about the pivotable connection between the first frame
306 and the second frame 308. The collapsible strut 310 is
simultaneously folded as the second frame 308 is raised.
Referring to FIG. 19, the second frame 308 is raised to a position
next to the first frame 306. Pin 324 is then installed to rigidly
connect the second frame 308 to the first frame 306. The hydraulic
boom hoist cylinders 34 are further retracted to swing the wire
rope guide 300 upwardly until it flips over center.
Referring to FIG. 20, the wire rope guide 300 is then lowered on to
the upper interior side of the boom butt 30 by extending the
hydraulic boom hoist cylinders 34. Pin 326 is then installed to
rigidly connect the first frame 306 of the wire rope guide 300 to
the upper interior side of the boom butt 30. The rigging platform
312 is then lowered into position.
Referring to FIG. 13, the boom top 28 and any boom inserts 32 are
assembled together on the ground adjacent to the boom butt 30.
Blocking 130 is typically used to support the boom top 28 and the
boom inserts 32 during the assembly process. The assembled boom top
28 and boom inserts 32 are then connected to the interior edge 84
of the end of the boom butt 30. The connections between the boom
butt 30, the boom top 28, and any boom inserts 32 can be one or
more of the connections shown in U.S. Pat. No. 5,199,586.
Referring to FIG. 14, the hydraulic boom hoist cylinders 34 are
retracted to lift the boom 26 to align the axis of the boom butt 30
with the axis of the assembled boom top 28 and any boom inserts 32.
The exterior edge 90 of the end of the boom butt 30 is then
connected to the assembled boom top 28 and any boom inserts 32 to
complete the assembly of the boom 26.
Referring to FIG. 15, the boom butt pendant 102 is disconnected and
preferably stowed on the mast 36. The boom pendants 42 are then
connected between the mast 36 and the boom top 28. The load hoist
lines 46 are then passed through the wire rope guide 50 and reeved
around the boom top sheaves 52. Finally, one or more hook blocks 54
are rigged to the load hoist lines 46 (as seen in FIG. 1).
Self-disassembly of the crane 10 is accomplished by following the
method described above in reverse order.
Normally, double-acting cylinders like cylinders 34 are powered by
open loop pumps, because the rod end of the cylinder takes less
fluid to move the piston than is displaced out of the piston end of
the cylinder. Open loop pumps draw hydraulic fluid from a reservoir
and fluid is returned from the cylinder to the reservoir. The
volume differential between the rod end and the piston end of the
cylinder can thus be easily accommodated.
However, open loop pumps are not as power efficient as closed loop
pumps, and turn much slower, delivering lower flow rates, than
comparable closed loop pumps. Also, comparable horsepower open loop
pumps are more expensive than closed loop pumps. Larger
displacement open loop pumps generally require super charging the
inlet either by pressurizing the reservoir or with a secondary
pump. The super charging pump must have the same flow rate as the
main open loop pump. Because of these drawbacks, a unique hydraulic
circuit using a closed loop pump was developed for crane 10. The
hydraulic circuit is shown in FIG. 21. As explained above, the
hydraulic cylinders 34 are preferably double-acting cylinders and
are used during normal crane operations to control the boom angle,
and during crane set up operations, particularly when installing
the upper counterweight assembly 62. When used to control the boom
angle during normal lifting operations, the cylinders 34 are
generally in tension. During the counterweight positioning
operation, the cylinders 34 are in compression. As a result, the
cylinders are sometimes controlled to move in a direction that is
natural for them to follow under the loads then being imposed. In
this situation, the pump is handling an overhauling load. That is,
the pump is motoring, or driving the diesel engine typically used
to drive the pump. In the preferred circuit, the pump is subject to
overhauling loads sometimes when the cylinders are extending and
sometimes when the cylinders are retracting.
The major components of the circuit include the closed loop pump
201, the double-acting cylinders 34, a charge pump 203, an
auxiliary pump 205, also referred to as an accessories pump because
it is also used to power auxiliary hydraulic accessories, a
cylinder directional control valve 225 and a replenish-hot oil
manifold, represented by dotted line 206, which incorporates a
relief valve 227 and a hot oil shuttle valve 229. The preferred
directional control valve 225 is a Model No. 4WE6J6X/EG12N9Z45 four
port, two solenoid valve from Mannesmann Rexroth. The preferred
replenish hot oil manifold 206 contains a hot oil shuttle valve
229, preferably Model No. DSGH-XHN, a relief valve 227, preferably
Model No. RPGC-LNN, and two check valves 241 and 242, preferably
Model No. CXFA-XAN, all in the form of cartridges that screw into
the manifold. The cartridges are from Sun Hydraulics.
The closed loop pump 201 and charge pump 203, and the other
components within dotted line 208, are preferably all built-in
components on a commercially available variable displacement pump,
such as the Series 90 pump from Sauer Sundstrand Corporation, Model
No. 90 L 100 KA 2 C 853 FI E 33 6BA 20 42 24. This pump
incorporates a directional flow control so that either of the two
ports 202 and 204 of the pump 201 can be alternatively used as the
discharge and intake ports. Alternatively, a closed loop pump with
unidirectional flow could be coupled to a separate directional flow
controller to interchangeably provide power to both sides of the
cylinders 34. The preferred closed loop pump includes internal
safety relief valves and other features which are not shown in FIG.
21 because they are conventional and form no part of the present
invention.
The cylinders 34 are preferably identical. As a result, the same
reference numbers are used to refer to the same parts of the
cylinders 34. Each cylinder 34 has a bore 236 and a piston 237
mounted in the bore 236, forming a piston end 238 of the cylinder
34. A rod 38 is connected to the piston 237 opposite the piston end
238. The rod 38 extends out of an exit end of the bore 236 but is
sealed at the exit end, forming a rod end 240 of the cylinder. A
first passageway 218 is in fluid communication with the piston end
238, and a second passageway 216 is in fluid communication with the
rod end 240 of the cylinder 34.
When the boom 26 is raised, the cylinders 34 are retracted. The
closed loop variable displacement pump 201 is brought on stroke to
pressurize lines 211, 212, 213 and 214. Fluid is allowed to enter
passageway 216 into the rod end 240 of each cylinder 34 through
check valves 224. The boom hoist directional control valve 225 is
electrically actuated to the boom up position in which flow from
the charge pump 203 in lines 210 and 215 passes through the boom
hoist directional control valve 225 and out lines 265 and 266 to
the pilot operated valves 221 mounted on each cylinder 34. The
pilot signal opens the pilot operated valves 221, allowing
hydraulic fluid to pass out of the cylinder bores 236 through
passageways 218. Lines 234, 232 and 231 return the fluid to port
202 of pump 201.
As the circuit is designed with a closed loop variable displacement
pump, the flow in the lines into and out of the cylinders 34 must
be equal at the pump 201. It would be best if the ratio of the
change in volume of the rod end to the change in volume of the
piston end as the rod is extended or retracted is between about 1:2
and about 1:1.1. In the presently preferred embodiment of the crane
10, the rod 38 has a diameter of 5.5 inches and a cross sectional
area of 23.8 square inches. The bore 236 has a diameter of 12
inches, and a cross sectional area of 113.1 square inches. The
preferred ratio of the change in volume of the rod end 240 to the
change in volume of the piston end 238 is thus (113.1-23.8):113.1
or 1:1.27. Thus, for one gallon of hydraulic fluid forced into
passageway 216, 1.27 gallons of hydraulic fluid comes out
passageway 218. The extra 0.27 gallons is drained from the circuit
through the replenish-hot oil manifold 206, out line 259 to the
cooler and ultimately back to the hydraulic reservoir, leaving one
gallon to return to port 202 of pump 201 through line 231. The
excess fluid is allowed out through line 233 in the replenish hot
oil manifold 206. The shuttle valve 229 is actuated by the pressure
in line 213 so that line 233 is connected to line 255. The fluid
then passes through line 257 and relief valve 227.
When the operator wants the boom 26 to go down, the pump 201 is
brought on stroke far enough to once again pressurize lines 211,
212 and 214 to a level sufficient to support the load. The boom
hoist directional valve 225 is electrically actuated to the boom
down (extend) position in which flow from the charge pump 203 in
line 215 passes through the boom hoist directional control valve
225 and out lines 263 and 264 to the pilot operated valves 223
mounted on each cylinder. The pilot signal opens the pilot operated
valves 223, allowing hydraulic fluid to pass out of the rod end 240
of the cylinders 34 through passageways 216. At this time, the flow
direction of the pump 201 is reversed, and port 202 becomes the
discharge port of pump 201. Flow passes through lines 231 and 234,
check valve 222, and passageway 218, causing the rod 38 to extend.
However, because the cylinder 34 is under tension, intake port 204
and lines 211 and 214 remain under high pressure.
As before, the flow into and out of each cylinder 34 must be equal
at the variable displacement pump 201. However, in the boom down
mode, one gallon of fluid from the rod end 240 of the cylinder 34
results in a need for 1.27 gallons to enter the piston end 238. The
0.27 gallons is made up from flow from the accessories pump 205
through the lines 251, 253 and 254 into the replenish-hot oil
manifold 206, which is positioned such that flow can enter line 233
from line 255 and join with the flow in line 231 to line 232, 234
and enter piston end 238. Since the cylinder 34 is generally in
tension during the boom-down operation, the lines 231, 232 and 233
are on the low pressure side of the pump 201. Hence, the make up
fluid is being supplied from the accessories pump 205 to the low
pressure side of the hydraulic circuit.
At very steep boom angles, the cylinders 34 may be in compression.
The hydraulic circuit of FIG. 21 allows for the closed loop pump to
handle extension under compressive loads as well, because as
discussed above the preferred crane 10 also uses the cylinders 34
for counterweight positioning operations.
During counterweight positioning operations, the cylinders 34 are
in compression. When the operator commands the cylinders to extend,
lines 231, 232, 233 and 234 become the high pressure side of the
circuit, feeding the piston end 238 of the cylinders 34 through
check valve 222. Port 202 becomes the discharge and high pressure
port on the closed loop pump 201. The boom hoist directional
control valve 225 is positioned so that pressure from the charge
pump 203 can flow through lines 215, 263 and 264 to open pilot
operated valves 223, allowing fluid to exit passageways 216. In the
extend mode, additional make up flow from the accessories pump 205
is brought through lines 251, 253 and 254 into the replenish-hot
oil manifold 206. The pressure in line 233 causes the pilot line to
operate valve 229 so that fluid may flow from line 255 into line
213 and then to join with the flow in lines 212 and 211 back to
pump 201 through port 204 on the pump. Once again, the make up
fluid supplied by the accessories pump 205 is fed into the low
pressure side of the hydraulic circuit.
When the operator commands the cylinders to retract during a
counterweight positioning operation, lines 231, 232, 233 and 234
remain the high pressure side of the circuit. Pump 201 is brought
on stroke far enough to once again pressurize these lines to a
level sufficient to support the load. The boom hoist directional
control valve 225 is electrically actuated to the retract position
so that flow from the charge pump 203 in line 215 passes through
the boom hoist directional control valve 225 and out lines 265 and
266 to the pilot operated valves 221 mounted on each cylinder 34.
The pilot signal opens the pilot operated valves 221, allowing
hydraulic fluid to pass out of the piston end 238 of the cylinders
34. At this time, the flow direction of the pump 201 is reversed so
that the rod 38 begins to retract. However, lines 231, 232, 233 and
234 remain the high pressure lines since the cylinder 34 is under
compression. Hence port 202 is the intake port, but is still the
high pressure port as well. Excess fluid from lines 212 and 214
passes out through line 213, valve 229, lines 255 and 257, relief
valve 227 and line 259 to the cooler and then on to the
reservoir.
The pilot operated valves 221 and 223 are mounted directly to the
cylinders. In the event of a hose burst, pilot pressure is lost.
The pilot operated valves then close, holding the cylinder in
place. Relief valves 226 and 228, on the other hand, allow excess
pressure that could damage the cylinders (such as from thermal
expansion when sunlight heats up the cylinder) to escape.
The pilot operated valves 221 and 223 are identical, and are
preferably Model No. DKJS-XHN valves cartridges from Sun
Hydraulics. These are what is known as pilot to open, two way
valves with an internal static drain. The relief valve 226 and the
check valves 222 are preferably both built into the same
commercially available Model SCIA-CCN cartridge from Sun
Hydraulics. Relief valve 228 and check valve 224 are likewise part
of one cartridge. All four cartridges are screwed into a single
manifold mounted to the middle of the cylinder. This manifold is
connected to the ends of the cylinder 34 by welded piping that is
an integral part of cylinder 34. Relief valves 228 are preferably
set at 5000 psi, and relief valves 226 are preferably set at 3000
psi. Any leakage from valves 228, 226, 223 and 221 is directed to
the low pressure reservoir, which is preferably a tank at
atmospheric pressure.
The accessories pump 205 is preferably one of three sections of a
gear pump Model 323 9639 161 from Commercial Intertech of
Youngstown, Ohio. Another section of this gear pump is the super
charge pump that supplies charge pump 203. In crane 10, the
accessories pump 205 is used to power components on the lower works
16 through line 252, such as jacking cylinders 104, as well as to
supply make-up fluid for the closed loop pump 201. Line 281 is a
pressure pilot line from a power beyond port of a valve on the
lower works. It is used to operate the piston of piston check valve
282 within the pump unload valve depicted by dotted line 280. The
pump unload valve also includes an orifice 283 which bleeds to
tank. A relief valve 285 is in parallel with the piston check valve
282. The relief valve 285 allows for pressure relief when pump 205
is running but fluid is not needed in line 252, but check valve 282
is not open. Normally, flow through line 251 is directed through
valve 282 because the power beyond valve provides a signal through
line 281 to open piston check valve 282. The orifice 283 allows
pressure to bleed out of line 281 so that check valve 282 can close
when fluid is desired to flow through line 252. A filter 270 cleans
the fluid as it flows out of the pump unload valve 280 so that
fluid entering the closed loop circuit through replenish-hot oil
manifold 206 is filtered. A check valve with substantial resistance
271 provides a parallel flow path to the hot oil manifold 206 if
filter 270 becomes blocked. Preferably a filter, not shown, is
provided between the supercharger and the charge pump 203. The
supercharger preferably provides hydraulic fluid at 75 psi.
If the charge pump 203 were large enough, it could be used to
supply the make-up fluid needed for the cylinder differential
through check valves 207 and lines 217 or 219. However, in the
preferred, commercially available variable displacement pump with
built in directional control 208, the built in charge pump 203 is
not large enough to perform that function, and thus the accessories
pump 205 is used.
The preferred hot oil shuttle valve 229 has pressure pilot lines
connected to lines 213 and 233 to automatically operate the shuttle
valve. When the pressure in line 233 is higher than the pressure in
line 213, line 255 will be connected to line 213. On the other
hand, when the pressure in line 213 is higher than the pressure in
line 233, line 255 will be connected to line 233.
Check valves 241 and 242 are included in the replenish hot oil
manifold 206 to take care of operating conditions in which the
pressure differential between lines 213 and 233 is insufficient to
open shuttle valve 229. This is likely to occur at steep boom
angles when the cylinder 34 are only in slight compression or
tension. During these situations, make up fluid from line 255 can
still enter the low pressure side of the circuit through check
valve 241 or 242, depending on whether line 258 or 256 has the
lowest pressure. Check valves 241 and 242, which have a slight
resistance, can also provide a parallel path for fluid to enter the
closed loop part of the circuit. When the shuttle valve 229 is
open, it will have a small pressure drop across it as fluid starts
to flow through it. When this pressure drop equals the slight
pressure needed to open the check valves 241 or 242, fluid will
take both paths. Shuttle valve 229, however, provides the normal
path by which fluid leaves the closed loop portion of the circuit
since check valves 241 and 242 only allow flow in one
direction.
Relief valve 227 is preferably set to open at 350 psi. This
maintains a minimum of 350 psi in the hydraulic circuit, which is
important because when accessories pump 205 is running and no fluid
is needed for the accessories or as make-up fluid in the closed
loop part of the cylinder circuit, the fluid from pump 205 will
unload through pump unload valve 280 and through lines 253, 254,
255 and 257. Relief valve 227 therefore maintains a minimum
pressure for pump 205. Pilot operated relief valve 209 similarly
provides a minimum pressure and relief for charge pump 203.
The hydraulic system is preferably controlled by a microprocessor
as part of the overall crane control function. Examples of control
systems for lift cranes using a microprocessor to control hydraulic
functions are disclosed in U.S. Pat. Nos. 5,189,605; 5,297,019 and
5,579,931, all of which are hereby incorporated by reference. As
such, the crane 10 will preferably include transducers to monitor
the fluid pressure at different points in the hydraulic system. The
control system, and the location of the transducers, is not within
the scope of the present invention.
In the preferred embodiment of the crane 10, the rod 38 is sized so
that it carries intended loads in compression. Since it is
desirable to keep the diameter of the rod 38 to a minimum, and
because the buckling strength of a rod decreases as its effective
length increases, the counterweight handling system is designed so
that the rods 38 only have to be operated with limited extension
while the cylinders 34 are in compression. This reduces the
potential buckling problem and allows the rods 38 to be designed
with smaller diameters than if the rods 38 could be fully extended
in compression. The tensile strength of the material used to make
the rods 38 is high enough so that even at this smaller diameter,
the rods 38 have sufficient tensile strength to safely handle
maximum expected tension loads.
The preferred hydraulic circuit described above allows a closed
loop pump to power the double-acting hydraulic cylinders 34. It
also provides that the extra fluid needed to make up for the
cylinder differential is always added to the low pressure side of
the circuit. Since the closed loop pump often handles overhauling
loads, sometimes the low pressure side of the circuit is connected
to the discharge port of the closed loop pump. The preferred
circuit takes this into account, and allows the make-up fluid to go
to the pump when the intake port is on the low pressure side, or go
to the cylinder when the pump intake port is on the high pressure
side. In this way the circuit can be used to operate the
double-acting cylinders in both a tension and compression
situation. Further, the pump supplying the make-up fluid can be
less expensive because it is always supplying to the low pressure
side of the circuit.
It should be appreciated that the apparatus and methods of the
present invention are capable of being incorporated in the form of
a variety of embodiments, only a few of which have been illustrated
and described above. The invention may be embodied in other forms
without departing from its spirit or essential characteristics. The
described embodiments are to be considered in all respects only as
illustrative and not restrictive, and the scope of the invention
is, therefore, indicated by the appended claims rather than by the
foregoing description. All changes which come within the meaning
and range of equivalency of the claims are to be embraced within
their scope.
* * * * *